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Ray Optics
Physical Science 101
11/07
Name ______________ Section ________
Partner’s Name _____________________
Purpose:
The purpose of this lab is to study the laws of reflection and refraction for flat
surfaces and to find out how converging lenses and converging mirrors can be used
to form real images.
Equipment:
ceiling tile, light source, 5 x 8 note card, object light, frosted glass, paper,
plane mirror, prism, protractor, straight pins, and thin lens
Part 1
Images from a Plane Mirror
i) to understand what is meant by the term optical image.
Procedure:
Locate the position of the image of a colored thumb tac in front of a mirror by
following the steps below.
1.
Place a sheet of paper on the ceiling tile. Put the plane mirror on the paper
with the object thumbtack 2 to 3 cm in front of the mirror. Don’t push the
thumbtack in all the way so you will be able to see the center pin of it when viewing
from the side. Draw a line outlining the surface of the mirror on the paper and a
circle around the object (thumbtack).
2.
Place an alignment pin anywhere a little to the left of the object and closer to
the mirror. Look into the mirror at the image of the object thumbtack along a line of
sight through the first alignment pin on the left (see head position on left side of
figure below). Place another alignment pin along your line of sight so that it, the
first alignment pin, and the image of the thumbtack are all along a straight line (see
figure below). Repeat this process for two alignment pins on the right side of the
object pin.
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Ray Optics
Figure 2
11/07
Mirror and Alignment Pins
3.
Remove the mirror from the paper.
4.
Draw a straight line through the left alignment pins that extends behind the
mirror. Draw a second straight line through the right alignment pins that also
extends behind the mirror. Make a circle where these two lines intersect and
label this the image.
5.
Measure the distance to the image from the reflective surface of the mirror,
di, and the distance to the object from the mirrors reflective surface, do.
di = ________________
do = ________________
Questions
1.
Are di and do equal?
2.
If you stand 10 ft in front of a plane mirror, how far away will your image
appear to be from you?
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Ray Optics
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3.
Real images are formed when the rays of light really come together on the
screen and virtual images are where the light appears to come from. Is the
image formed by a plane mirror real or virtual?
4.
In you walk towards a mirror with a speed of 2 m/s how fast do you and your
image approach each other?
ii)
Periscope. Arrange two mirrors as shown in the top view below (the grey
side is the reflecting side of the mirror.
Prediction: When viewing through this arrangement as shown what will you
see?
Test your Prediction: When viewing through this arrangement what do you see?
http://cs.clark.edu/~mac/PHSC101/images/ABCD1line.JPG
With different colors of line types (solid, dotted, dashed) draw rays in the figure
above from each letter that you see reflecting from each mirror to the viewing area
near your eyes.
Is the right to left order reversed or maintained with the periscope?
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Ray Optics
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Part 2. Refraction through a piece of glass.
i. Viewing your thumb. Lay a thick piece of glass flat side down on a piece of
paper. Look at your thumb or figure through the glass as shown in the top view at
left below.
Top view
Side view
Describe what you observe. Use the sketch below to show the position of your
thumb as viewed through the glass relative to that observed through the air above
the glass plate.
ii. More careful measurements. Use a pencil to trace around the edges of the
glass. Place two alignment pins on one side of the glass so the line connecting these
makes an angle (1) of about 50 to 60 degrees with the normal line to the edge of
the glass. (see dark circles below in the top view below.) Place two additional
alignment pins on the other side of the glass so that the line connecting these two
also lines up with the apparent line of the first two as viewed through the glass.
(see light circles below.)
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Ray Optics
11/07
1=____________
2=____________
3=____________
4=____________
Complete the figure above on you paper by drawing 1) a line through the first two
alignment pin points to point a on the glass; 2) a line through the last two alignment
pin points to point b on the glass; 3) a line from a to b 4) and finally the two line
normal to the glass at points a and b.
With a protractor carefully measure  1,  2,  3, and 4 and record above. The
index of refraction, n, for glass can be calculated using Snell’s law.
sin( 1) = n sin ( 2)
or
n= sin(q1)/sin(q2)=
You will need a scientific calculator to do this. If you don’t have on try the online calculator at.
http://my.hrw.com/math06_07/nsmedia/tools/Sci_Calculator/Sci_Calculator.html
n =_____________________
The index of refraction describes how much faster light travel in a vacuum than in
the glass. The speed of light in a vacuum is 300,000,000 m/s. What is the speed of
light in this glass?
Speed of light in glass= _________________________
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Ray Optics
Part 2
11/07
Light Refraction through a Prism
Purpose: to show that white light is composed of a spectrum of colors and that
each color of light interacts with the prism material differently.
When light travels through a transparent object its speed is reduced relative to
its speed in a vacuum. This change in speed can cause bending or refraction of
light. When you look into a pool of water things appear at different positions than
they actually occupy. The light coming to your eye from the underwater object is
bent.
A very ‘colorful’ phenomena has to do with the fact that different colors of
light have different speeds in transparent objects. The following steps will help you
determine what color of light moves fastest, slowest, and how this determines what
rainbows look like. The index of refraction is related to the refraction angle of the
incident light beam. The greater the angle of refraction, the greater the index of
refraction.
Procedure:
1
Shine a ray of light
from
.
the light source
through
.
a prism.
.
The
. figure to the right
is a top view looking
down from above the
table.
2.
Hold a card up on the other side of the prism and adjust the prism until you
can see a rainbow on the card.
3.
Sketch below the rainbow and indicate the colors.
1.What color is refracted through the
largest angle by the prism? Smallest?
2.What color has the largest index of
refraction? Smallest?
3. Which color travels faster in glass?
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GEOMETRIC OPTICS
FOCUSED ENLIGHTENMENT
“RAYS-ED” IMAGES
The first investigation concerns the angle between light rays from an
object which reach a detector. Below is a sketch of an eye and
the silhouette of the disk. Light rays from the edges of the disk
to the eye are shown. What happens to the angle between the
rays as the disk moves away from the eye?
Suppose the disk were a mile away, what would the angle between the
rays be like? If the disk were a thousand miles away? On the Sun
(93 million miles away)?
If the rays were approximately parallel, how far away would the disk
be?
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Place the multi-slit mask in the ray box and
adjust the slide on the box to make the rays
parallel. This is most simply done by shining
the rays along the lines on the graphs. We
will use this configuration for the next few
experiments.
LENS
Place the ray box on the left and the biconvex lens on the silhouette on
the graph. With the parallel rays from the left passing through the
lens, sketch where the light rays go. Measure the distance from the
center of the lens to the point where the light rays converge (+ if to
the right of the lens, - to the left).
length = ______________ cm.
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LENS
As before, place the lens on the silhouette with the light coming from
the left. Draw in lines where the light rays go. If the actual rays don’t
cross at a point, extend them back with dotted lines to find a crossing
point. As before, measure the length from the lens center to the
crossing point. Use a negative sign if the intersection is for the dotted
lines.
length = _____________ cm.
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Ray Optics
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REFLECTIONS ON MIRRORS
With the light from the left, place the curved mirror on the curves,
reflective side to the left, and sketch the light rays, as before.
Measure the distance from the center of the mirror to the intersection
point, recording a – sign if the intersection is behind the mirror.
length = _____________ cm.
length = _____________ cm.
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